FIELD OF THE INVENTION
The present invention, generally, concerns computer graphic systems and, more particularly, relates to a new and improved image generator to produce images in real time more realistically and at less expense.
Image generators are digital computer graphics systems used to produce imagery for real time training, such as flight simulation, and for amusement and other applications. Image generators produce perspective images from stored mathematical descriptions of objects, usually polygon approximations to the shapes of real objects.
The image generator produces discrete color samples, called pixels, that form a rectangular two-dimensional output image. The image is typically converted to a video raster to drive a cathode ray tube or other display.
The number of pixels in each row and column of the display determines the maximum possible resolution of the image. High resolution is critical to many of the applications of visual simulation.
For military simulations, the resolution determines the range at which targets may be detected in the simulator. Usually, the resolution afforded by the simulator is less than that of the human eye, so that training is impaired by reduced detection and recognition distances.
In commercial flight simulation, pilots would like sufficient resolution to identify runway stripes, markings and lights at the same distances as in the real world. Again this places a premium on the resolution of the image generator.
Unfortunately, the cost of an image generator increases significantly as the resolution of its output increases. Typically, one-half to two-thirds of the cost of an image generator is associated with generating pixels.
Doubling the resolution (both horizontally and vertically) requires four times as many pixels be generated per unit time. Consequently, that part of the image generator is made approximately four times as expensive. Overall, the image generator becomes 2.5 to 3 times as expensive.
One of the attempted solutions to the problem of increased cost is called "target insetting." This solution uses a projector that portrays moving military targets, typically enemy aircraft, at high resolution, while the non-target background imagery is projected separately at lower resolution.
The term "target" is used here to mean any object of special interest with respect to its detection, recognition, or identification. This would include, for example, runway features in a commercial airline simulator or air traffic in a simulator to train control tower operators.
A target projector must be moved by a servo-mechanism, so that a target is placed in a correct position relative to the background image as the target is moved about in the scene. Sometimes a circular portion of the background image is darkened electronically to accept such an inset target image, and other times, the target is projected significantly brighter than the background imagery.
Electromechanical target insetting is virtually impossible to accomplish with such precision that the inset is imperceptibly different from the background in both color and illumination. Consequently, there is a potential problem in a trainee being able to detect the insetting artifact and, subsequently the target, more easily than the target resolution alone otherwise would allow.
The cost of an electromechanical mechanism for such a target projector is substantial, and therefore, it is difficult to justify the cost premium of high resolution in this form of image generator.